Masahiko Taguchi

HiSIM2: Advanced MOSFET Model Valid for RF Circuit Simulation

The compact MOSFET model development trend leads to models based on the channel surface potential, allowing higher accuracy and a reduced number of model parameters. Among these, the Hiroshima University Semiconductor Technology Academic Research Center IGFET Model (HiSIM) solves the surface potentials with an efficient physically correct iteration procedure, thus avoiding additional approximations without any computer run-time penalty. It is further demonstrated that excellent model accuracy for higher-order phenomena, which is a prerequisite for accurate RF circuit simulation, is achieved by HiSIM without any new model parameters in addition to those for describing the current-voltage characteristics

MOSFET harmonic distortion analysis up to the non-quasi-static frequency regime

MOSFET harmonic distortion characteristics up to the cutoff frequency (fT) are measured and analyzed with the MOSFET model HiSIM. While distortion characteristics at low frequency are determined by carrier mobility, characteristics at high frequency are influenced by the time delay of carriers to form the channel. At low frequency, IP3 values, calculated using a quasi-static model, correspond to values from the conventional method of extraction. For accurate prediction of IP3, non-quasi-static effects become necessary at high-frequency switching above fT/2

Modeling of Carrier Transport Dynamics at GHz-Frequencies for RF Circuit-Simulation

Carrier dynamics in a MOSFET channel under fast time-varying gate input is included in the modeling for circuit simulation and implemented in SPICE3f5 at only 7% increased computational runtime cost. Correct reproduction of transient drain currents as well as harmonic-distortion characteristics are verified. While the carrier dynamics under low-frequency operation is mostly governed by the carrier mobility in the channel, the dominant factor under high-frequency operation changes to channel charging and discharging.

Analysis and Compact Modeling of MOSFET High-Frequency Noise

We have developed a high-frequency noise model for short channel MOSFETs by considering the position dependent surface potential which results in a non-uniform mobility distribution along the channel. The chosen approach successfully reproduces the induced-gate noise and the cross-correlation noise between drain and gate for short channel MOSFETs without additional model parameters. In particular, the gate noise characteristics at GHz frequencies are accurately captured. The newly developed high-frequency noise model is implemented in the complete surface-potential based MOSFET model HiSIM (Hiroshima-university STARC IGFET Model) for circuit simulation

Gate-length and drain-voltage dependence of thermal drain noise in advanced metal-oxide-semiconductor-field-effect transistors

The high thermal-drain-noise coefficient γ for short-channel metal-oxide-semiconductor-field-effect transistors (MOSFETs) has little to do with hot electrons or velocity saturation, but is determined by the potential gradient along the channel. Consequently, an analytical model for circuit simulation, derived by integration with the surface-potential distribution along the channel, reproduces measured noise characteristics without additional fitting parameters. Furthermore, experimental and theoretical data suggest a fixed relation between the source-drain voltage (Vds) gradients of γ under the saturation condition and the threshold-voltage shift (ΔVth) relative to a long-channel MOSFET.

Surface-Potential-Based Metal-Oxide-Silicon-Varactor Model for RF Applications

We have developed a surface-potential-based metal–oxide–silicon (MOS)-varactor model valid for RF applications up to 200 GHz. The model enables the calculation of the MOS-varactor capacitance seamlessly from the depletion region to the accumulation region and explicitly considers the carrier-response delay causing a non-quasi-static (NQS) effect. It has been observed that capacitance reduction due to this non-quasi-static effect limits the MOS-varactor application to an RF regime.

On the validity of conventional MOSFET nonlinearity characterization at RF switching

We analyze the linearity of metal oxide semiconductor field effect transistors (MOSFETs) at radio frequency switching using the conventional extraction method of IP3, measured harmonic distortion (HD), and a surface-potential-based MOSFET model for circuit-simulation. The applicability of the conventional extraction method of IP3 at low frequency to represent IP3 at high frequency is also investigated. At low frequency, measured HD characteristics and extracted IP3 values correspond to the prediction by the model which adopts the quasistatic approximation, i.e., instantaneous carrier response is assumed. Beyond half of the cutoff frequency, the carrier response delay enhances the MOSFET nonlinearity, which is manifested by a decreased first order harmonic and a pronounced curvature of the third order harmonic. Consequently, the conventional extraction method of IP3 value from the intersection point of linearly extrapolated first and third harmonics becomes unreliable

Non-quasi-static approach with surface-potential-based MOSFET model HiSIM for RF circuit simulations

We develop a non-quasi-static MOSFET compact model suitable for simulating RF circuits operating under GHz frequency. The model takes into account the carrier dynamics by incorporating the time delay for the carriers to form a channel. Both the time-domain and frequency-domain expressions are successfully derived from the same basic equation by using the proposed modeling methodology, and the consistency of the both representations are verified. The model accuracy in predicting transient currents is demonstrated by comparing with simulation results of a 2D device simulator. The developed NQS model is implemented into SPICE3f5 and achieves stable circuit simulations with only 3% simulation time increase.

Frequency Dependence of Measured Metal Oxide Semiconductor Field-Effect Transistor Distortion Characteristic

Non-linearity of metal oxide semiconductor field-effect transistor (MOSFET) characteristics induces harmonic distortions, which causes serious problems for RF analog applications. Features of the harmonic distortions are investigated experimentally under high frequency operations. Comparison of measured harmonic distortions with inter-modulation distortions concludes that the harmonic distortions are frequency dependent under high frequency operations. A reason for this is enhanced contribution of the displacement, which is originally frequency dependent.

Noise Modeling Based on Self-Consistent Surface-Potential Description for Advanced MOSFETs aiming at RF Applications

We have developed MOSFETs noise models for the 1/f, thermal and induced-gate noise based on self-consistent surface-potential description. Consideration of non-uniform mobility and carrier distributions arising from the surface potential distribution along the channel is indispensable for accurate noise modeling for RF applications. The developed noise models are implemented in the complete surface-potential based MOSFET model HiSIM (Hiroshima-university STARC IGFET Model) for circuit simulations